1. Field of the Invention
The present invention relates to an optical fiber drawing method and apparatus, in which reduction in optical fiber strength due to surface injuries or the like of an optical fiber glass preform can be suppressed.
2. Description of the Related Art
FIG. 6 is a side view showing the configuration of a conventional drawing apparatus. In the apparatus, an optical fiber glass preform 1 is grasped by a feeder 2, and the forward end portion of the optical fiber glass preform 1 is heated and melted while the optical fiber glass preform 1 is fed into a drawing furnace 3, and then drawn by a capstan 24 so that an optical fiber 5 is drawn. In this case, the feeder is supported by an appropriate supporting member (not shown) through a screw 7. Generally, after passing through the drawing furnace 3, the optical fiber 5 is passed through a diameter monitor 21 for monitoring the diameter thereof. Thereafter, the optical fiber 5 is passed through a coating die 22 to be coated with an appropriate resin. Then, the optical fiber 5 is wound by a take-up bobbin 4 through a curing furnace 23, a capstan 24 and a proof tester 25. The curing furnace 23 sets the resin applied to the optical fiber 5 at the coating die 22. Incidentally, the proof tester 25 gives a predetermined tension to the optical fiber 5. If a portion of the optical fiber does not has a sufficient strength, the portion is broken when the portion passes through the proof tester 25.
Thus obtained quartz glass fiber having a diameter of 125 .mu.m generally has breaking strength of about 7 kg. In an actual case, however, micro injuries or foreign matters are generated or deposited respectively in or on the surface of the glass in the process of production, so that portions of low strength exist in the longitudinal direction. Further, the foreign matters deposited on the surface cause not only reduction in strength but also deviations in outer diameter.
Accordingly, in order to remove injuries or foreign matters on the surface of glass, measures are taken so that an optical fiber glass preform is subjected to etching with chemicals or to flame abrasion treatment. Further, deposition of foreign matters is prevented by making the cleanliness of production atmosphere high.
Even if the surface of an optical fiber glass preform is subjected to etching with chemicals or to flame abrasion treatment after production of the glass preform, new injuries or foreign matters may be generated or deposited to cause reduction of strength in handling till the optical fiber glass preform is mounted on the drawing apparatus. Therefore, it is not always possible to obtain a satisfactory result.